In recent years, techniques for packaging a semiconductor integrated circuit with high density are being developed to meet a demand for versatile and compact electronic devices. As one of such packaging techniques, there has been proposed a system-in-package (SiP) semiconductor device of chip-on-chip (CoC) type in which semiconductor chips are stacked and mounted together. This semiconductor device draws attention in that it is excellent in realizing a thin package (see, e.g., patent document 1: Japanese Patent Application Laid-open No. Hei 11-3969).
When stacking semiconductor chips one above another, use is made of, e.g., a method by which each semiconductor chips severed from a wafer are bonded together in a stacked state. However, this method, i.e., the method for producing a stacked body of semiconductor chips by bonding each semiconductor chips together, suffers from an increase in the number of processes and requires a lot of time and labor for manufacture of a large number of stacked semiconductor chips. This poses a problem in that it is impossible to enhance productivity.
As a solution to this problem, there has been proposed a method for manufacturing a system-in-package semiconductor device in which semiconductor wafers are bonded together prior to dicing them into each semiconductor chips. This method will be described now.
Referring first to FIG. 11A, a first semiconductor wafer 510 provided with connector portions 511 and a second semiconductor wafer 520 provided with connector portions 521 are prepared and positioned together so that the connector portions 521 correspond to the connector portions 511. The first and second semiconductor wafers 510 and 520 are bonded together to obtain a semiconductor wafer bonded body 530 (see FIG. 11B).
Then, the semiconductor wafer bonded body 530 is diced as shown in FIG. 11B. This produces a stacked semiconductor chip 560 as shown in FIG. 11C, namely a bonded body consisting of a semiconductor chip 540 severed from the first semiconductor wafer 510 and a semiconductor chip 550 severed from the second semiconductor wafer 520, in which the connector portions 511 and the connector portions 521 are electrically connected together.
As shown in FIG. 11D, the semiconductor chip bonded body 560 is then mounted on an interposer 630 having a wiring pattern 640 and bumps 620 in such a manner as to make contact with the wiring pattern 640, thereby manufacturing a system-in-package semiconductor device 100.
Here, the bonding of the first semiconductor wafer 510 and the second semiconductor wafer 520 in FIG. 11A can be performed by, e.g., compressing the first semiconductor wafer 510 and the second semiconductor wafer 520 together with an anisotropic conductive film (ACF) interposed therebetween. In this method for bonding the semiconductor wafers 510 and 520 with the anisotropic conductive film, electrical connection between the connector portions 511 and 521 is obtained by mutual contact of metal particles contained in the anisotropic conductive film, i.e., point-to-point contact between the metal particles.
If the semiconductor device 100 is operated in this state, a resin component contained in the anisotropic conductive film is expanded or contracted due to heat generated from the semiconductor chip bonded body 560 or a change in an ambient temperature. As a result, distances between the metal particles are changed. In some cases, the metal particles moved in a thickness direction of the anisotropic conductive film come into a non-contact state, thereby changing a resistance value between the connector portions 511 and 521 or breaking conduction between the connector portions 511 and 521. In the method for bonding the semiconductor wafers 510 and 520 with the anisotropic conductive film, therefore, there is a problem in that it is impossible to obtain stable conduction between the connector portions 511 and 521.